1. Field of the Invention
The present invention relates generally to a deviation detecting and compensating method and apparatus for an information reproducing apparatus, which reproduces information recorded on a recording medium, or an information recording apparatus, which records information on a recording medium, and more specifically to a deviation detecting and compensating method and apparatus for detecting and compensating a deviation in a servo control system, such as a tilt servo control system, a tracking servo control system, a focus servo control system or the like.
2. Description of the Related Art
In an information reproducing apparatus for reproducing information recorded on an optical disk or an information recording apparatus for recording information on an optical disk, some kinds of servo controls are carried out. For example, a tracking serve control is carried out in order to control the spot position with respect to a track on the optical disk. A focus servo control is carried out in order to control a focal distance of the light beam. A tilt servo control is carried out in order to control a tilt between the surface of the optical disk and the optical axis of the light beam.
Generally, in such servo control systems, a deviation or error is obtained by comparing an actual amount (measured amount) corresponding to an actual spot position, focal distance or tilt with a desired amount such as a reference voltage. Then, the actual spot position, focal distance or tilt is adjusted so as to reduce the deviation. If the deviation is reduced to zero, the actual spot position, focal distance or tilt becomes correct.
However, it is difficult to eliminate deviations completely for the following reason. Optical disks have a various different deviations, such as out-of-roundness, eccentric location of the center hole, warp etc.. Therefore, the different deviation occurs for each optical disk. Furthermore, if the optical disk has warp partially, degree of the deviation is different between the inner circumference and the outer circumference of the optical disk.
A number of solutions of this problem has been proposed. For example, a possibility of eliminating such deviations is shown in Japanese patent application laid open (KOKAI), No. 8-129769.
However, these solutions needs complex calculations and learning functions. It is difficult to carry out the calculations and the learning functions rapidly. As quickness is important to the servo control systems in the information reproducing apparatus or the information recording apparatus, it is necessary to eliminate such deviations not only completely but also rapidly with respect to each optical disk.
It is therefore a first object of the present invention to provide a method and apparatus for detecting a deviation in a servo control system, which can detect the deviation accurately and rapidly.
A second object of the present invention is to provide a method and apparatus for compensating a deviation in a servo control system, which can compensate the deviation completely and rapidly.
The aforementioned first object can be achieved by a deviation detecting method of the present invention. The deviation detecting method has the processes of: applying a disturbance signal, which has a wave form having a constant frequency, to a controlled system; detecting a variation in a wave form of an output signal output from the controlled system by comparing the wave form of the output signal with the wave form of the disturbance signal; and detecting the deviation on the basis of the detected variation.
In an electrical or optical servo control system and its controlled system, the wave form of the output signal output from the controlled system varies depending on the presence of the deviation. The variation of the wave form of the output signal can be detected by comparing this wave form with a standard wave form. Then, the deviation can be detected on the basis of this variation.
More specifically, the disturbance signal is applied to the controlled system. The disturbance signal has a wave form having a constant frequency. This signal serves as the standard signal.
As the disturbance signal is applied to the controlled system, the output signal from the controlled system has a wave form. If there is a deviation, the wave form of the output signal varies.
This variation is detected by comparing the wave form of the output signal with the wave form of the disturbance signal. Then, the deviation is detected on the basis of the detected variation.
Thus, the deviation in the servo control system can be accurately detected without any complex calculations or any learning functions. Since neither complex calculation nor leaning function is used, the deviation can be rapidly detected.
In the aforementioned deviation detecting method, the variation detecting process may has the processes of: detecting a first timing that a level of the disturbance signal reaches a first level; detecting a second timing that a level of the output signal reaches a second level; and detecting the variation in the wave form of the output signal by comparing the first timing with the second timing. Therefore, the deviation in the servo control system can be accurately detected by a simple construction.
Furthermore, in the aforementioned deviation detecting method, it is desirable that the first level is an average of the level of the disturbance signal, and the second level is an average of the level of the output signal. Therefore, the detection process can be carried out easily. Alternatively, the second level may be a peak of the level of the output signal.
Moreover, in the aforementioned deviation detecting method, the variation detecting process may has the processes of: generating an envelope of the output signal; and detecting a variation in a wave form of the envelope by comparing the wave form of the envelope with the wave form of the disturbance signal. Therefore, the detection process can be carried out easily.
The aforementioned second object can be achieved by a deviation compensating method of the present invention. The deviation compensating method has the processes of: applying a control signal, which is a direct current signal, to a controlled system; adding a disturbance signal, which has a wave form having a constant frequency, to the control signal; detecting a variation in a wave form of an output signal output from the controlled system by comparing the wave form of the output signal with the wave form of the disturbance signal; detecting the deviation on the basis of the detected variation; and varying a level of the control signal on the basis of the detected deviation so as to reduce the detected deviation.
In this deviation compensating method, deviation in the servo control system is detected by the same method as the aforementioned deviation detecting method. Then, the level of the control signal is adjusted on the basis of the detected deviation.
Thus, the deviation in the servo control system can be accurately detected without any complex calculations or any learning functions. Since neither complex calculation nor leaning function is used, the deviation can be rapidly detected. As a result, the deviation can be compensated completely and rapidly.
The aforementioned first object can be also achieved by an deviation detecting apparatus of the present invention. The deviation detecting apparatus has: an applying device for applying a disturbance signal, which has a wave form having a constant frequency, to the controlled system; a variation detecting device for detecting a variation in a wave form of an output signal output from a controlled system by comparing the wave form of the output signal with the wave form of the disturbance signal; and a deviation detecting device for detecting the deviation on the basis of the detected variation.
In an electrical or optical servo control system and its controlled system, the wave form of the output signal output from the controlled system varies depending on the presence of the deviation. The variation of the wave form of the output signal can be detected by comparing this wave form with a standard wave form. Then, the deviation can be detected on the basis of this variation.
More specifically, the disturbance signal is applied to the controlled system. The disturbance signal has a wave form having a constant frequency. This signal is the standard signal.
As the disturbance signal is applied to the controlled system, the output signal from the controlled system has a wave form. If there is a deviation, the wave form of the output signal varies.
This variation is detected by comparing the wave form of the output signal with the wave form of the disturbance signal. Then, the deviation is detected on the basis of the detected variation.
Thus, the deviation in the servo control system can be accurately detected without any complex calculations or any learning functions. Since neither complex calculation nor leaning function is used, the deviation can be rapidly detected.
In the aforementioned deviation detecting apparatus, the variation detecting device may includes: a first timing detecting device for detecting a first timing that a level of the disturbance signal reaches a first level; a second timing detecting device for detecting a second timing that a level of the output signal reaches a second level; and a wave form variation detecting device for detecting the variation in the wave form of the output signal by comparing the first timing with the second timing. Therefore, the deviation in the servo control system can be accurately detected by a simple construction.
Furthermore, in the aforementioned deviation detecting apparatus, it is desirable that the first level is an average of the level of the disturbance signal, and the second level is an average of the level of the output signal. Alternatively, it is desirable that the second level is a peak of the level of the output signal. Therefore, the detection process can be carried out easily.
Moreover, in the aforementioned deviation detecting apparatus, the variation detecting device has: an envelope generating device for generating an envelope of the output signal; and an envelope variation detecting device for detecting a variation in a wave form of the envelope by comparing the wave form of the envelope with the wave form of the disturbance signal. Therefore, the detection process can be carried out easily.
The aforementioned second object can be achieved by an deviation compensating apparatus of the present invention. The deviation compensating apparatus has: a control signal applying device for applying a control signal, which is a direct current signal, to the controlled system; a disturbance signal adding device for adding a disturbance signal, which has a wave form having a constant frequency, to the control signal; a variation detecting device for detecting a variation in a wave form of an output signal output from the controlled system by comparing the wave form of the output signal with the wave form of the disturbance signal; a deviation detecting device for detecting the deviation on the basis of the detected variation; and a varying device for varying a level of the control signal so as to reduce the detected deviation.
In this deviation compensating apparatus, deviation in the servo control system is detected by the same manner as that in the aforementioned deviation detecting apparatus. Then, the level of the control signal is adjusted on the basis of the detected deviation.
Thus, the deviation in the servo control system can be accurately detected without any complex calculations or any learning functions. Since neither complex calculation nor leaning function is not used, the deviation can be rapidly detected. As a result, the deviation can be compensated completely and rapidly.
The nature, utility, and further feature of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.